The present invention refers to a combustion chamber device, including a combustion chamber and a set of burners which each has an outlet opening in the combustion chamber.
In such combustion chambers with several burners, for instance gas turbines, acoustic pressure oscillations, or pressure pulsations might arise, which lead to mechanical oscillations creating strength problems and noise problems. Such oscillations may have an oscillation frequency at some or several hundreds of Hz and is, in combustion chambers for gas turbines, an increasing problem, at least partly due to the more severe requirements of lower emissions of, for instance, NOx compounds. A possible explanation to the increase of the oscillations when the emissions decreases could be that a fuel of a main flow and the air are premixed and form a mixture in which the combustion thereafter will take place. The better and more uniform mixture, the lower is the percentage of emissions, but at the same time the burning volume is more susceptible for pressure oscillations. Since combustion chamber devices today frequently include a plurality of burners which influences each other via any common space, such as a combustion chamber, the oscillations from different burners will in many cases also intensify each other.
It is known that the influence of such acoustic pressure oscillations at least partly may be reduced by the supply of fuel in a so-called pilot flow, i.e. a fuel which is not pre-mixed. However, the combustion of such a pilot flow results in an increase of the emissions.
DE 4 336 096 discloses an annular combustion chamber with a plurality of burners. The burners are displaced in relation to each other in a longitudinal direction in order to reduce the oscillations. All the burners seem to have an identical shape.
WO 98/12479 discloses a combustion chamber for a gas turbine with a number of burners of different sizes. However, each burner has a maintained geometrical shape, i.e. all measure relations have been maintained although the size is changed.
The object of the present invention is to reduce the influence of the acoustic pressure oscillations which are generated during operation of a combustion chamber device without, at the same time, increasing the emissions of, in the first place, nitrogen oxides.
This object is obtained by the combustion chamber device initially defined, in which each burner includes members for the supply of a flow of an oxygen-containing gas to the burner, members for the supply of a fuel to the burner and a space, which extends to the combustion chamber along a longitudinal direction and is arranged to enable the mixture of the fuel supplied and the oxygen-containing gas supplied, wherein each burner is arranged to convey a substantially equally large flow of oxygen-containing gas through the burner to the combustion chamber, wherein each burner is defined by at least one parameter, which includes a characteristic length of the space along the longitudinal direction, and wherein at least the characteristic length of at least one of said burners is selected in such a way that it deviates from the corresponding length of another burner in said set, and in such a way that the influence of the oscillations which arise during operation of the combustion chamber device are reduced.
By changing the geometry of the burners in such a way and by giving the burners an asymmetric or irregular characteristic it is possible to obtain different frequencies of the oscillations which are generated at different burners, which substantially reduces the risk that the oscillations which are generated in different parts of the combustion chamber device will intensify each other. Instead, the probability that at least a part of the oscillations will interfere in such a way that they are reduced, or even attenuate each other, increases. Consequently, the invention creates the possibilities of determining, by calculations, such a value of the characteristic length for at least one of the burners that the influence of the oscillations which arise during operation of the combustion chamber device are substantially reduced. A change of the length of the space or the burner may be obtained in an easy manner. The combustion chamber construction is not influenced by such a change of one or several burners. By designing all of the burners in such a way that they are arranged to convey an essentially equally large flow or an equally large quantity of oxygen-containing gas through the burner to the combustion chamber, the oscillation reducing effect may be obtained in an easy manner since each burner may be controlled with respect to the fuel supply as if they were identical.
According to an embodiment of the invention, each burner extends between a rearward end portion, which includes said members for the supply of an oxygen-containing gas, and a forward end portion, which includes said outlet opening. Thereby, the whole space may be utilised for giving the flow of oxygen-containing gas the desired properties, as to obtain an effective mixture with the fuel. Thereby, said members for the supply of a fuel may be provided upstream the forward end portion and in particular at the rearward end portion. However, said members for the supply of fuel may also include a distribution member which is provided in the space downstream the rearward end portion. Advantageously, the space and the characteristic length extend from the rearward end portion to the outlet opening. It is also possible to let the space and the characteristic length extend from said members for the supply of a fuel to the outlet opening.
According to a further embodiment of the invention, said parameter includes a characteristic width of the space. The characteristic width may extend perpendicularly to said longitudinal direction of said space. Advantageously, the space has an elongated shape, i.e. the characteristic length is substantially greater than the characteristic width. Furthermore, the space may have an essentially circular cross-sectional shape transversally to the longitudinal direction and be substantially cylindrical.
According to a further embodiment of the invention, the characteristic width of at least one of said burners is selected in such a way that it deviates from the corresponding width of another burner in said set. By such a geometric variation, the possibilities are further increased to reduce the pressure pulsations in an effective manner.
According to a further embodiment of the invention, said parameter includes a distance from the burner in question to the closest adjacent burner and wherein said-distance from at least one of said burners to the most closely adjacent burner is selected in such a way that it deviates from a corresponding distance between two other adjacent burners in said set.
According to a further embodiment of the invention, said parameter for at least two of said burners is selected in such a way that it deviates from the corresponding parameter for another burner in said set. By varying the geometry of several burners, the possibilities are increased to reduce the oscillations or the pressure pulsations. Thereby, said parameter for a plurality of said burners may be selected in such a way that it deviates from the corresponding parameter for another plurality of said burners in said set. Of course, it is also possible to let any of said parameters be different for essentially every burner of a combustion chamber device according to the invention.
According to a further embodiment of the invention, the device is arranged to be provided upstream of a gas turbine and to supply hot combustion gas to the gas turbine. Such an application is advantageous since the problem of the oscillations is serious, especially in connection with gas turbines. Thereby, the combustion chamber may be annular or ring-shaped, and extend around an axis of rotation of a gas turbine along a substantially circular path.
According to a further embodiment of the invention, the burners of said set are provided along the substantially circular path, wherein said parameters also include a distance from said burners to the substantially circular path and wherein this distance of at least one of said burners is selected in such a way that it deviates from the corresponding distance of another burner in said set.